This paper investigates a super-regenerative oscillator (SRO) operating at 61.5GHz with a novel quenching technique to maximize the power efficiency. The circuit includes a pulse generator, which generates the SRO quench signal with a tunable duty cycle enabling an improved energy efficiency. To prove the concept, the circuit is implemented in a 130nm SiGe BiCMOS technology with a total chip area of 0.96mm2. Measurement results show that the quench duty cycle can be tuned from 60% to 15%. The oscillator has a tuning range of 12 %, from 57.3 to 64.6GHz. The SRO exhibits an input sensitivity of -40dBm and an output power of up to 5dBm, which results in a maximum regenerative gain of 45dB. A maximum quenching frequency of 3GHz is demonstrated. Depending to the duty cycle, the circuit exhibits a dc power consumption of down to 13mW and achieves a record DC-to-RF power efficiency of 21.7%. To the best knowledge of the authors, this is the first SRO that includes a quench pulse generator with an externally tunable duty cycle and thus enables dynamic optimization of the dc power consumption. Compared to state of the art, the SRO achieves by far the highest power efficiency and the largest oscillation tuning range.